How do intensity-based and character fitting approaches differ in converting images to ASCII art in C ?

Image to ASCII Art Conversion in C

Introduction

Converting an image to ASCII art involves converting each pixel in the image to a character that approximates its intensity or shape. This article explores two approaches for this conversion using C :

Approach 1: Intensity-Based Conversion

• Pixel/Area Intensity Based (Shading):

  • Divides the image into pixels or rectangular areas (dots)
  • Computes the average gray scale intensity of each dot
  • Replaces each dot with a character whose intensity is closest to the computed intensity

• Character Map:

  • Precomputed list of characters with their corresponding intensities
  • Characters can be distributed linearly or arbitrarily

Code Example:

<code class="c++">AnsiString m = ".,:;ox%#@&";
for (int y = 0; y < bmp->Height; y++) {
    for (int x = 0; x < bmp->Width; x++) {
        int i = (p[x + x + x + 0] + p[x + x + x + 1] + p[x + x + x + 2]) / 3;
        i = (i * m.Length()) / 768;
        s += m[m.Length() - i];
    }
    s += endl;
}</code>

Approach 2: Character Fitting (Hybrid Approach)

• Tries to match image areas with characters of similar intensity and shape

• Step-by-Step Process:

  • Divide image into rectangular areas
  • Compute intensity of each area in multiple zones (left, right, up, down, center)
  • Create a character map with similar intensity zones
  • Find the closest matching character in the map and replace the image area

Code Example:

<code class="c++">int xs, ys, xf, yf, x, xx, y, yy;
int i, i0, d, d0;
DWORD **p = NULL, **q = NULL;

for (;;) { // Dynamic allocation error handling
    // Font Properties
    xf = font->Size;   if (xf < 0) xf = - xf;
    yf = font->Height; if (yf < 0) yf = - yf;

    // Character Map
    for (x = 0, d = 32; d < 128; d++, x++) {
        map[x].c = char(DWORD(d));
        tmp->Canvas->TextOutA(0, 0, map[x].c);
        map[x].compute(q, xf, yf, 0, 0);
    }

    // Main Loop
    xf -= xf / 3;
    xs -= xs % xf;
    ys -= ys % yf;
    for (y = 0; y < ys; y += yf, txt += eol)
        for (x = 0; x < xs; x += xf) {
            gfx.compute(p, xf, yf, x, y);
            i0 = 0; d0 = -1;
            for (i = 0; map[i].c; i++) {
                d = abs(map[i].il - gfx.il) +
                    abs(map[i].ir - gfx.ir) +
                    abs(map[i].iu - gfx.iu) +
                    abs(map[i].id - gfx.id) +
                    abs(map[i].ic - gfx.ic);
                if ((d0 < 0) || (d0 > d)) {
                    d0 = d; i0 = i;
                }
            }
            txt += map[i0].c;
        }
    break;
}</code>

Comparison and Example:

Approach	Advantage	Disadvantage
Intensity-Based	Simple, Fast	Limited Visual Appeal
Character Fitting	Higher Quality Output	Slower Processing

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